A music signal may include one or both of an instrumental portion and a vocal portion. The invention herein is directed to a system which can remove the vocal portion of a recorded music signal and add to the remaining instrumental portion, a vocal and/or instrumental signal introduced via a microphone. Alternatively, such systems can simply playback the entire reproduced signal from a recording/reproducing disk (hereinafter simply referred to as a "recording disk" or a "disk"). Such systems may be referred to as a voice changing system or apparatus.
As used herein, a music signal with no vocal portion is referred to as a play signal or a play portion. The vocal portion of a music signal is known as a sound signal or a sound & portion. Further, a so-called multi-sound disk is one in which a play signal only is stored in the left channel and play and sound signals are stored in the right channel. A stereo disk is one in which only play signal or both play and sound signals are stored in both right and left channels.
FIG. 3 is a block diagram showing the construction of a conventional voice changing apparatus.
In FIG. 3, an output signal of a microphone is supplied to a microphone input terminal I.sub.M. The left and right channel music signals reproduced from a disk or the like are applied respectively to input terminals I.sub.L and I.sub.R. The signals to be supplied to the input terminals I.sub.L and I.sub.R are previously demodulated by a known demodulating apparatus (not shown). Reference numerals O.sub.L and O.sub.R respectively designate output terminals of the left and right channels.
A microphone input detecting circuit 1 detects that the sound signal is supplied to microphone input terminal I.sub.M from the microphone. To prevent malfunction caused by external noise, the microphone input detecting circuit 1 has a band pass filter (BPF) for passing only frequencies within the band of the human voice and a level detecting circuit for detecting a human sound level. When the microphone input detecting circuit 1 detects the sound signal, it outputs a switching signal for controlling switch 2B, described later.
A multi-sound voice changing circuit 2 consists of a balance resistor 2A connected at both ends thereof to input terminals I.sub.L and I.sub.R, and switch 2B for changing its contact from contact b to contact a upon receiving a changing signal from the microphone input detecting circuit 1. The switch 2B outputs the music signal, including the play and sound signals passing through the balance resistor 2A, when no changing signal is received and, on the other hand, outputs the play signal recorded in the left channel of the disk when the changing signal is received.
A stereo voice changing circuit 3 has band eliminating filters (BEFs) 3A and 3B for removing an intermediate frequency range such as 200 Hz to 4 KHz for example from the music signals of the left and right channels, & and has subtracting amplifier 3C for subtracting the music signal of the right channel from the music signal of the left channel to cancel the sound signal and reproduce the play signal. Stereo voice changing circuit 3 also has BPF 3D for passing the play signal outputted from subtracting amplifier 3C through an intermediate frequency range thereof, and has adder 3E for adding the play signal outputted from BPF 3D to the play signal outputted from BEF 3A to provide a play signal of the left channel. Stereo voice changing circuit 3 further has adder 3F for adding the play signal outputted from BPF 3D to the play signal outputted from BEF 3B to provide a play signal of the right channel.
In the stereo voice changing circuit 3 thus constructed, the sound signal recorded at an intermediate frequency range of the music signal is the same in phase in each of the left and right channels and is eliminated by the subtracting amplifier 3C. The remaining signal, having a frequency outside the intermediate frequency range of the filters 3A and 3B passes to the outputs of the filters. That is, the music signal without a sound signal, i.e., a play signal only can be obtained.
Selecting switch 4 selects the music signals of input terminals I.sub.L and I.sub.R, and multi-sound voice selecting switch 5 selects the music or play signal outputted from multi-sound voice changing circuit 2. Stereo voice selecting switch 6 selects the play signal outputted from stereo voice changing circuit 3.
Left adder 7L and right adder 7R add an input signal of microphone input terminal I.sub.M to the music signals of input terminals I.sub.L, I.sub.R, the music or play signal outputted from multi-sound voice changing circuit 2, or the play signal outputted from stereo voice changing circuit 3. The music signal outputted from left adder 7L is supplied to output terminal O.sub.L and the music signal outputted from right adder 7R is supplied to output terminal O.sub.R.
The operation of the above-mentioned apparatus will next be described.
First, when it is desired to listen to the music signals supplied to input terminals I.sub.L and I.sub.R, without any signal removal, selecting switch 4 is closed (turned on) and simultaneously, multi-sound voice selecting switch 5 and stereo voice selecting switch 6 are open (turned off). Thus, the music signals supplied to input terminals I.sub.L and I.sub.R are supplied to output terminals O.sub.L and O.sub.R as they are.
When the above-mentioned apparatus is to be used as an instrumental accompaniment player and the recording disk is a multi-sound disk, selecting switch 4 and stereo voice selecting switch 6 are turned off and, simultaneously, multi-sound voice selecting switch 5 is turned on. In this condition, if no sound signal is supplied to microphone input terminal I.sub.M, switch 2B remains switched onto the side of contact b, and accordingly, the music signals supplied to input terminals I.sub.L and I.sub.R are supplied to output terminals O.sub.L and O.sub.R through multi-sound voice changing circuit 2 as they are.
When a sound signal is supplied to microphone input terminal I.sub.M, a switching signal is supplied to switch 2B from microphone input detecting circuit 1 so that switch 2B is switched onto the side of contact a. In this condition, the music signal at input terminal I.sub.L, i.e., a play signal only, is supplied to adders 7L, 7R through multi-sound voice changing circuit 2. Accordingly, adders 7L and 7R add the sound signal supplied to microphone input terminal I.sub.M to the play signal outputted from multi-sound voice changing circuit 2 and supply the added signal to output terminals O.sub.L and O.sub.R. Therefore, the play signal from the multi-sound disk which serves as background instrumental music to the vocals added by the microphone.
When the apparatus is to be used as an instrumental accompaniment player and the reproducing disk is a stereo disk, selecting switch 4 and multi-sound voice selecting switch 5 are turned off while stereo voice selecting switch 6 is turned on. In this condition, stereo voice changing circuit 3 outputs the play signal only derived by eliminating sound signal from the music signal, to adders 7L and 7R. When a sound signal is supplied to microphone input terminal I.sub.M, first adders 7L and 7R add the microphone sound signal supplied to microphone input terminal I.sub.M and the play signal outputted from stereo voice changing circuit 3 to thereby output a music signal which is supplied to output terminals O.sub.L and O.sub.R.
Therefore, the play signal, derived by eliminating the sound signal from the music signal, serves as background music, and is added to the microphone sound signal. That is, multi-sound voice changing circuit 2 and stereo voice changing circuit 3 act as a sound signal eliminating circuits, which eliminate sound signals in accordance with an interrelationship of recorded channels.
In the conventional voice changing apparatus constructed as above, the respective switches 4 to 6 must be set to predetermined operating states in accordance with the purpose of usage and the type of the reproducing disk used. In actual operation, this becomes complicated.
Further, when the respective switches 4 to 6 are incorrectly set, the apparatus cannot operate as intended.